Characterization of NH overtone and combination bands in the near-infrared absorption spectra of simple cyclic imides

✍ Scribed by Patrick J. McNeilly; Tariq A. Andrea; S.Edward Krikorian

• Publisher: Elsevier Science
• Year: 1992
• Tongue: English
• Weight: 447 KB
• Volume: 48
• Category: Article
• ISSN: 1386-1425
• DOI: 10.1016/0584-8539(92)80151-l

✦ Synopsis

Bands due to overtone and combination vibrational modes attributable to the imide grouping have been elucidated in the near-IR absorption spectra of small-ring cyclic imides, in which the grouping is in a c/s, ct~ conformation. The spectra closely parallel the spectra of c/s lactams except that two combination modes involving the carbonyl stretching fundamental, [v(NH) + v(C=O)] and [2v(C=O) + imide III], occur at higher wavenumbers in the imide spectra, reflecting the higher frequency at which this fundamental absorbs. This same factor results in a reversal in the wavenumber positions of the [2v(C=O) + imide III] and [v(NH) + imide III] combination bands in the imide spectra relative to those in the lactam spectra. In addition, in-phase and out-of-phase vibrational coupling between the two carbonyl groups in the imides may compound the band due to the [v(NH)+ v(C=O)] combination mode. These three spectral characteristics serve to distinguish the imides from the lactams in the near-IR.